1. Field of the Invention
The present invention relates to a surface-mounting technique of electronic devices and more particularly, to a surface-mounting structure and method of electronic devices such as resistors, capacitors, diodes, transistors, integrated circuit devices (ICs) and the like onto the surface of a circuit medium such as a printed circuit board, a ceramic substrate and the like.
2. Description of the Prior Art
Conventionally, on mounting operation of a surface-mounting electronic device onto the surface of a printed circuit board, a well-known soldering technique as shown in FIG. 1 has been developed and practically used in a variety of application fields.
As shown in FIG. 1, first, a solder paste 115 is coated on a mounting pad 112 which is formed on the surface of a circuit board 111. Next, a terminal 114 of a surface-mounting electronic device 113 is placed onto the coated solder paste 115. Then, the solder paste 115 is temporarily melted by the application of heat and then cooled, thereby connecting the terminal 114 to the pad 112 by the solder joint 115.
Also, a mounting technique for a printed circuit board using face fasteners was disclosed in the Non-Examined Utility-Model Publication Nos. 60-176588 and 4-55149.
FIG. 2 shows a method of easily bonding a couple of faces by face fasteners, which was disclosed in the Non-Examined Utility-Model Publication No. 60-176588.
In FIG. 2, a face fastener 222 is stuck onto a flat bent-up part formed by cutting and raising a chassis 221. Another face fastener 224 is stuck onto the bottom side of a printed circuit board 223. Electronic parts 225 are mounted on the top side of the board 223. The exposed hooks of the two face fasteners 222 and 224 are mutually joined or linked by pressing them. Thus, the printed circuit board 223 is fixed to the flat bent-up part of the chassis 221.
FIG. 3 shows another method of easily bonding a couple of faces by face fasteners, which was disclosed in the Non-Examined Utility-Model Publication No. 4-55149.
In FIG. 3, curled members 332 made of a thermally conductive material are fixed thickly on a surface of a heat-radiation plate 331, thereby forming a face fastener. Curled members 334 made of a thermally conductive material are fixed thickly on a surface of a heat-radiation plate 333, thereby forming another face fastener. These two face fasteners are forced to adhere to each other while applying a thermally conductive grease 335, interlocking and connecting the plates 331 and 333.
In the above conventional face fastener techniques, which should naturally be capable of freely attaching and detaching the fasteners, the face fasteners are connected by mutually locking the curled or hooked members under the application of pressure. The connected fasteners are disconnected by causing elastic deformation in the curled or hooked members with a tensile force to thereby release their mutual locking.
The above conventional mounting structures have the following problems.
With the above conventional bonding method using the solder paste shown in FIG. 1, a process of applying the solder paste onto the mounting pads is necessary before placing the surface-mounting devices on the circuit board. Furthermore, the solder paste has many factors to adversely affect the workmanship of the surface-mounting structure. For example, placement error of the devices, and tombstone (Manhattan) phenomenon where the devices undesirably rise due to uneven melting of the solder paste on heating or the like readily take place. This makes the surface-mounting process complex, thereby not only complicating the process control but also giving rise to problems with connection accuracy and reliability.
On the other hand, if the above fastener technique is applied to the connection between a terminal of an electronic device and a mounting pad of a circuit board, the formation of fine curled, hooked, or barbed members of an electrically conductive material is necessary on the metal faces of the terminal and pad. As electrically conductive materials, a variety of metals, electrically conductive plastics, and resins mixed with an electrically conductive filler have been well known. However, whichever the electrically conductive material may be used, it is technically quite difficult to form a curled, hooked, or barbed shape on the metal face, thus raising a problem of unsuitability to industrial applications.
Furthermore, the curled, hooked, or barbed members used in the above conventional fastener technique facilitate the face-to-face connection and disconnection through their forced elastic deformation. Thus, another problem that the necessity of appropriate elastic deformation limits the material selection range.